Once a wellbore has been drilled and one or more zones of interest have been reached, a well casing is run into the wellbore and is set in place by injecting cement or other material into the annulus between the casing and the wellbore. The casing, cement and formation are then perforated to enable flow of fluid from the formation into the interior of the casing.
In the past, the casing, cement and formation have been perforated using bullets or shaped charges. Both techniques, however, may result in a perforation having a positive skin, i.e. localized decreased permeability that reduces the production of formation fluid from the formation into the perforation. It is generally desirable that the perforations have a neutral or a negative skin, i.e. localized increased permeability resulting in an increased production of formation fluid. In addition, these traditional perforating methods rely on the use of explosives, which pose obvious safety, transportation and security issues.
Known perforating techniques, as well as drilling techniques, do not provide any analysis of the formation rock being perforated or drilled. More so, there is no known technique for analyzing the chemical elements and certain other chemical characteristics of formation rock in situ, that is, without removing the rock from the well. Such analysis would be helpful in determining the optimal location and depth for the current and other perforations, provide in-situ formation evaluation at the perforation site, or on a larger scale, assist in evaluating the current well or other wells. Presently, to obtain an analysis of the formation rock being perforated or drilled, a representative sample of the formation rock must be retrieved to the surface and analyzed. Depending on whether the analysis can be performed on site, such analysis may add days or even weeks to the well completion. Further, the analysis involves material that may have been altered in the process of removing it from the well.